Earth's Interior and Geological Dating Techniques

Definitions

• Principle of Actualism: Analyzing present processes is key to interpreting past events.
• Relative Dating: Establishes the order of events without numerical ages.
• Absolute Dating: Provides numerical ages for events (e.g., years or millions of years ago).
• Stratification Planes: Surfaces that delimit layers (strata).
• Roof: The uppermost and youngest part of a stratum.
• Wall (Base): The lowermost and oldest part of a stratum.
• Series Roof: The top and youngest part of a series of strata.
• Series Wall: The bottom and oldest part of a series of strata.
• Thickness: The vertical distance between the roof and wall of a stratum.
• Polarity Criteria (Roof-Wall): Sedimentary structures that help determine the orientation of strata.
• Concordance: Two materials are concordant if the surface separating them is parallel to the stratification planes of both.
• Facies: Lithological and paleontological features that indicate the origin and environment of a rock.

Methods for Studying Earth's Interior

Direct Methods

Through observation of areas where materials from Earth's interior reach the surface (e.g., volcanoes), we obtain data about the Earth's interior.

Indirect Methods

Characteristics of the interior are inferred from data of diverse nature, such as the behavior of earthquake-generated waves.

• Mines: Excavations for mineral extraction.
• Surveys: Holes drilled into the ground.
• Geothermal Gradient: The variation of Earth materials' temperature with depth.
• Density: A body's mass divided by its volume.
• Seismic Method: The procedure that has provided the most information about Earth's deep structure.
• Seismicity (Earthquakes): Ground vibrations generated by the release of energy accumulated in rocks under stress.
• Fault: A fracture in rocks where relative motion has occurred between blocks.
• Focus (Hypocenter): The point where an earthquake originates.
• Epicenter: The point on Earth's surface closest to the earthquake focus.
• Seismic Waves: Vibrations generated at the focus that propagate in all directions.